To reduce blood flow into aneurysms, surgeons often insert a flow
diverter - tiny tubes made of weaved metal, like stents - across the
opening of an aneurysm. With the blood flow into the aneurysm reduced,
the risk of rupture is minimized.

If the opening, or neck, of an aneurysm is large, surgeons will
sometimes overlap two diverters, to increase the density of the mesh
over the opening. Another technique is to compress the diverter to
increase the mesh density and block more blood flow.

‘Using high performance computing to examine how to best treat aneurysms, researchers determined that a single, compressed diverter produced a dense mesh that covered 57% of a fusiform-shaped aneurysm, and proved to be more effective than overlapping two diverters.’

However, the old adage about two being better than one doesn't necessarily
apply to brain surgery.
That's according to a study performed by University at Buffalo engineers
that used high performance computing to examine how to best treat
aneurysms.

But which technique is better?

A computational study published in January in American Journal of Neuroradiology
points to the single, compressed diverter provided that it produces a
mesh denser than the two overlapped diverters, and that it covers at
least half of the aneurysm opening.

The research, which is ongoing, could eventually help doctors determine the best way to treat patients suffering from aneurysms.

"When doctors see the simulated blood flow in our models, they're
able to visualize it. They see that they need to put more of the dense
mesh here or there to diffuse the jets (of blood), because the jets are
dangerous," said Hui Meng, a mechanical engineering professor at UB and
lead author of the study.

Meng holds appointments in UB's School of Engineering and
Applied Sciences and the Jacobs School of Medicine and Biomedical
Sciences. She is also co-director of the Toshiba Stroke Research Center
at UB.

Using UB's supercomputer

Working with UB's supercomputing facility, the Center for
Computational Research, Robert Damiano and Nikhil Paliwal, both PhD
candidates in Meng's lab, used virtual models of three types of
aneurysms - fusiform (balloons out on all sides), and medium and large
saccular (balloons on one side) - and applied engineering principles to
model the pressure and speed of blood flowing through the vessels.

The engineers modeled three different diverter treatment methods -
single non-compacted, two overlapped, and single compacted - and ran
tests to determine how they would affect blood flow in and out of the
aneurysm using computational fluid dynamics.

"We used equations from fluid mechanics to model the blood flow, and
we used structural mechanics to model the devices," Damiano said. "We're
working with partial differential equations that are complex and
typically unsolvable by hand."

These equations are converted to millions of algebraic equations and
are solved using the supercomputer. The very small size of the mesh
added to the need for massive computing power.

"The diverter mesh wires are 30 microns in diameter," Paliwal said.
"To accurately capture the physics, we needed to have a maximum of 10 to
15 micron grid sizes. That's why it is computationally very expensive."

Compressed versus overlapped

The models showed that compressing a diverter produced a dense mesh
that covered 57% of a fusiform-shaped aneurysm. That proved more
effective than overlapping two diverters.

The compacted diverter was less effective in saccular aneurysms. As
diverters are compressed, they become wider and bump into the sides of
the vessel, so they could not be compressed enough to cover a small
opening of an aneurysm. Compression was more effective in a large necked
saccular aneurysm, producing a dense mesh that covered 47% of
the opening.

Complete coverage of an aneurysm using a solid diverter is not
favorable because a porous scaffold is needed to allow cell and tissue
growth around the neck of the aneurysm, Paliwal said. In addition, the
danger of blocking off smaller arteries prevents the use of solid
diverters.

Next, as part of a National Institutes of Health-funded project, the
team wants to look back over hundreds of previous cases, to determine
how blood flow was affected by the use of diverters. The idea is to
build a database so that more definitive conclusions can be drawn.

"We're going to look at and model previous cases, and hopefully we'll
have a way to determine the best treatment to cause the best outcome
for new aneurysm cases," Damiano said.

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